1. Field of the Invention
This invention relates to a digital signature method and to an information communication system.
2. Related Background Art
Computers and computer networks have recently come into wide use; and because of this they can be implemented in a manner to carry out social activity. However, in this situation, there is a problem of invasion of individual privacy.
One method for carrying out social activity while protecting privacy is that of maintaining anonymity.
By using public key cryptography, a sender can send information only to an intended receiver, and the receiver can be certain of the identity of the sender.
By using a technique known as "zero knowledge proof", it is possible for one person who has information to prove to another person that he/she has certain information while the information itself remains confidential.
An information communication system which uses such technique is described in a publication by Masahiro Mambo and Eiji Okamoto entitled "A Method to Publicly Specify a Signer With Hiding Identity", (The 18th Symposium on Information Theory and its Applications--October 1995).
In this specification, the above described information communication system is referred to as the "MO System".
Also in this specification, cryptographic techniques such as "Public Key Cryptography", "Zero Knowledge Proof", "MO System" and "Digital Signature Method" will be described below in order.